Method of forming an upset on the end of a tube



J1me 1962 e. E; MOHNKERN ETAL 3,038,251

METHOD OF FORMING AN UPSET ON THE END OF A TUBE I Filed NOV. 20, 1957 A2 I /3 E D /0 /4 INVENTORS GERALD E. MOH/VKERN and RAYMOND LSTO/VE Attorney United States Patent Office 3,038,251 METHOD OF FGRMING AN UPSET ON THE END @F A TUBE Gerald E. Mohnkern and Raymond L. Stone, Gil (lily,

Pa, assignors to United States Steel 'Qorporation, a corporation of New Jersey Filed Nov. 20, 1957, Ser. No. 697,554 1 Claim. (Cl. 29-534) This invention relates to a method of forming an upset on the end of a tube, and to the resulting article of manufacture.

The invention is particularly applicable to hollow sucker rods used in the petroleum industry for actuating a reciprocating pump at the bottom of a well, but is not thus limited, and has broader application wherever similar problems are encountered. Sucker road ends are forged to produce upsets which are threaded to engage couplings. Although most sucker rods are solid, hollow rods are used where there is need to inject material into the well, for example, to combat corrosion or to dilute extremely viscous oils. The ends of hollow rods cannot be forged like solid rods since their bores become distorted or even completely blocked. Therefore conventional practices have been to thread the end of hollow rods without first upsetting them or else to weld preformed joint sections to the rod ends. Neither practice is fully satisfactory. Threading without upsetting reduces the cross-sectional area of a rod and hence weakens it, while welding often induces improper stresses or creates areas subject to corrosion. Another possibility is to forge an upset on the end of a hollow rod and then drill out the distorted bore, but this practice has the objection that it leaves a nick in the bore surface where stresses are concentrated and breakage can occur.

An object of our invention is to provide an improved method of forming an upset on the end of a tube, which method overcomes the difiiculties of prior practices and produces a more satisfactory article.

A more specific object is to provide an improved method of forming an upset on the end of a tube in which the bore through the tube is plugged with a solid piece of greater length than the portion affected by the forging operation, the end of the tube is forged to form an upset, and the solid piece subsequently drilled out.

A further object is to provide, as an improved article of manufacture, a tube whose end is upset, but which is free of objectional welding stresses and has at least equal tensile strength to the rest of the tube. In the drawingi FIGURE 1 is a longitudinal section of the end portion of a tube prepared for forming an upset in accordance with our invention;

FIGURE 2 is a longitudinal section showing the upset partially forged;

FIGURE 3 is a longitudinal section showing the forging step completed; and

FIGURE 4 is a longitudinal section of the end portion of a completed sucker rod formed in accordance with our invention.

FIGURE 1 shows the end portion of a metal tube 10, for example of steel, which has a bore 12. A closely fitting cylindrical plug 13 of similar metal is inserted within the bore and extends from the end of the tube to a point beyond the portion of the tube affected by the sub sequent forging operation. Although the exact length of v e plug is not critical, typically it terminates one to four inches beyond the portion of the tube gripped by the forg- 3,538,251 Fateinted June 12, 1962 ing dies. Next the end portion of the tube is heated to a suitable forging temperature and shaped in conventional forging equipment, not shown, to furnish an upset of the desired configuration. In the example of a sucker rod, a partial upset 14 of configuration shown in FIGURE 2 can be formed in the first forging pass, and a complete upset 15 of configuration shown in FIGURE 3 in subsequent forging passes. As the tube is forged, heat and pressure weld the plug 13 to the tube throughout the portion which the forging dies grip. The inner portion of the plug beyond the dies remains closely fitting within the bore, but does not become Welded.

After the forging operation is completed and the tube cooled, plug 13 is drilled out to form a bore 16, as shown in FIGURE 4. Bore I6 is drilled concentrically with bore 12, but is of slightly smaller diameter. The unwelded inner portion of the plug remains and forms an integral sleeve 17 closely overlying the extremity of the weld uniting the plug and tube. Thus the weld is enclosed and fully protected against corrosion and there are no exposed crevices at the weld. Sleeve 17 also serves to distribute stresses which might otherwise be concentrated where the drilled hole intersects the tube bore. After threads 18 are cut in the upset, there still are no points at which the cross-sectional area of the tube is less than its original area.

From the foregoing description, it is seen that our invention affords a simple method of forming an upset on the end of a tube without the disadvantages of prior methods. The completed tube is fully protected against corrosion at the welds, and has an undistorted bore achieved without reduction in cross-sectional area.

While we have disclosed only a preferred way of practicing our method and a preferred embodiment of the article, it is apparent modifications may arise. Therefore We do not wish to be limited by the disclosure set forth, but only by the scope of the appended claim.

We claim:

In the manufacture of hollow sucker rods which have a continuous bore adapted to carry fluid into a well, a method of forming the end portion of a rod comprising inserting within the bore of a metal tube a solid closely fitting cylindrical plug of similar metal of a length less than that of said tube bore and extending from the end of said tube thereinto for a distance equal to the length of said plug, forging an upset on the plugged end portion of said tube and thereby welding an adjacent portion of said plug within said tube but leaving unwelded a portion of the plug remote from the end of the tube and beyond the upset, drilling a bore entirely through said plug to provide communication between the plugged end of the tube and the portion of its bore beyond said plug, the unwelded portion of said plug remaining in closely fitting relation with the tube bore and covering the inner extremity of the weld and distributing stresses Within the tube bore, and externally threading a portion of said upset.

References Cited in the file of this patent UNITED STATES PATENTS 1,357,475 Rigby Nov. 2, 1920 1,526,880 Tannehill Feb. 17, 1925 1,753,638 Axtell Apr. 8, 1930 1,966,602 Wahlsteen July 17, 1934 2,047,555 Gardner July 14, 1936 2,227,436 Buckwalter Jan. 7, 1941 2,557,722 Brauchler June 19, 1951 

